224
FXUS63 KLSX 270813
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
313 AM CDT THU MAR 27 2025
KEY MESSAGES
- INTERMITTENT SHOWERS AND THUNDERSTORMS BRING AN END TO OUR DRY
STRETCH TODAY. A FEW STRONGER THUNDERSTORMS WILL THREATEN HAIL
UP TO QUARTER-SIZED THIS AFTERNOON AND EARLY EVENING NORTH OF
I-70.
- FRIDAY WILL BE LARGELY DRY AND BREEZY, BUT MORE SHOWERS AND A
FEW WEAK THUNDERSTORMS ARE FORECAST SATURDAY BEFORE A LARGER
SYSTEM THREATENS STRONG TO SEVERE THUNDERSTORMS SUNDAY.
- AFTER A VERY WARM END TO THE WEEK, PARTICULARLY FRIDAY, MARCH
WILL VERY LIKELY (90%+ CHANCE) END WITH A NOTICEABLE 15-20
DEGREE COOLDOWN MONDAY BEFORE TEMPERATURES MODERATE MID-WEEK.
SHORT TERM
(THROUGH LATE FRIDAY AFTERNOON)
ISSUED AT 311 AM CDT THU MAR 27 2025
A WING OF 850-700MB WARM AIR ADVECTION INTERACTING WITH INCREASED
MOISTURE AND WEAK FRONTOGENESIS IN THE SAME LAYER IS FORCING WEAK
SHOWERS ACROSS NORTHERN MISSOURI AND WESTERN ILLINOIS. FURTHER WEST
IN THE CENTRAL/SOUTHERN PLAINS, SURFACE OBSERVATIONS INDICATE A
DEVELOPING WARM FRONT EXTENDING INTO A WEAK SURFACE LOW LEE OF THE
ROCKIES IN CENTRAL COLORADO. THE LOW IS FORMING AMIDST A WEAK MID-
LEVEL SHORTWAVE EMBEDDED UNDER A LONGWAVE RIDGE OVER THE FRONT
RANGE. THE WAVE WILL GRADUALLY DRIFT EAST INTO THE SOUTHERN PLAINS
TODAY AS THE RIDGE ITSELF ALSO EXPANDS AND LOSES AMPLITUDE A BIT.
THE RESULTANT HEIGHT RISES IN ADDITION TO PERSISTENT SURFACE TO
850MB WAA WILL DRAW THE WARM FRONT NORTH AND EAST INTO THE MID-
MISSISSIPPI VALLEY THROUGH THE DAY. IT IS LIKELY THAT THERE WILL BE
A NOTEWORTHY TEMPERATURE GRADIENT FROM SOUTHWEST TO NORTHEAST DUE TO
THE FRONT'S PASSAGE, WITH HIGH TEMPERATURES RANGING FROM AROUND 80
DEGREES IN CENTRAL/SOUTH-CENTRAL MISSOURI TO ROUGHLY 60 DEGREES IN
SOUTH-CENTRAL ILLINOIS.
HIGH-RESOLUTION GUIDANCE CONTINUES TO SUPPORT A DEVELOPING PLUME OF
500-1250 J/KG OF MUCAPE IN THE VICINITY OF THE FRONT BEGINNING EARLY
THIS AFTERNOON, SUPPORTING AT LEAST SCATTERED THUNDERSTORMS. WHILE
THERE REMAINS SOME UNCERTAINTY AS TO WHERE THESE WILL BE, THE
CONSENSUS POSITION OF THE FRONT SUGGESTS THE BEST THREAT TO BE NORTH
OF I-70 STARTING IN THE LATE MORNING THROUGH THE EARLY EVENING.
WHILE CONVECTION MAY NOT BE CONSTANTLY IMPACTING ANY ONE LOCATION,
STORM MOTIONS WILL BE PARALLEL TO THE WARM FRONT. THIS ORIENTATION
SUPPORTS MULTIPLE WAVES OF THUNDERSTORMS DIRECTLY ALONG AND AHEAD OF
THE BOUNDARY, LIKELY IN NORTHERN MISSOURI AND WEST-CENTRAL ILLINOIS
WHERE THE FORECAST RAIN CHANCES ARE HIGHEST. THE STOUT WAA WILL ALSO
PROMOTE A STRONG CAPPING INVERSION TO KEEP THE CONVECTION LARGELY
ELEVATED IN THE ABSENCE OF ANY SIGNIFICANT FORCING. WHILE MOST OF
THE THUNDERSTORMS WILL REMAIN SUB-SEVERE WITH MID-LEVEL LAPSE RATES
STAYING IN CHECK UNTIL AFTER THE FRONT IS CLEAR OF THE REGION, ONE
OR TWO MORE ROBUST UPDRAFTS MAY STILL THREATEN MARGINALLY-SEVERE
HAIL IN THE NORTHERN HALF OF THE FORECAST AREA THIS AFTERNOON INTO
THE EARLY EVENING.
ACTIVITY WILL WANE OVERNIGHT WITH FRONT LIFTING NORTHEAST, AIDED BY
A STRENGTHENING LOW-LEVEL JET. THE STRENGTHENING WINDS AND LOW-LEVEL
WAA WILL BOLSTER TEMPERATURES OVERNIGHT, POTENTIALLY AS MUCH AS 15
DEGREES WARMER THAN THE NIGHT BEFORE IN SOME LOCATIONS. BY SUNRISE
FRIDAY, THE REGION WILL VERY LIKELY (90% CHANCE) BE DRY AND REMAIN
THAT WAY THROUGH THE EVENING. THE SURFACE PRESSURE GRADIENT WITHIN
THE OPEN WARM SECTOR APPEARS TO STRENGTHEN AMONG MOST GUIDANCE
THROUGH THE MORNING, SUPPORTING AN UPTICK IN SUSTAINED WINDS AND
GUSTS. WHILE WIND ADVISORY CRITERIA WINDS (30MPH+ SUSTAINED OR
45MPH+ GUSTS) LOOK UNLIKELY (LESS THAN 10% CHANCE), EXPECT 15-20MPH
SUSTAINED WINDS WILL GUSTS TO 30MPH ON FRIDAY OUT OF THE SOUTHWEST.
FRIDAY ALSO LOOKS TO BE THE WARMEST DAY OF THE FORECAST PERIOD
AMIDST THESE STRONG SOUTHWEST WINDS, WITH THOSE LEE OF THE OZARKS
(EVEN ST. LOUIS) INCREASINGLY LIKELY TO APPROACH 80 DEGREES AND THE
REST OF THE REGION WELL WITHIN THE MID/UPPER 70S.
MRB
LONG TERM
(FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 311 AM CDT THU MAR 27 2025
BY LATE FRIDAY EVENING, THE WEAK UPPER-LEVEL WAVE STUCK AMIDST THE
BROADER RIDGE WILL INTERACT WITH ANOTHER WEAK WAVE UPSTREAM TO
AMPLIFY SOMEWHAT AND BRING OUR NEXT CHANCE FOR RAIN TO THE REGION.
BY THIS POINT, A PLUME OF PRECIPITABLE WATER THAT IS MODELED NEAR
THE 90TH CLIMATOLOGICAL PERCENTILE WILL EXIST ACROSS MOST OF THE
REGION, PER GLOBAL ENSEMBLES. THAT SAID, THE FORCING AND LIFT
AVAILABLE TO THAT MOISTURE IS NEBULOUS AND WEAK. THE BEST OVERLAP OF
EVEN MARGINAL ASCENT, FORCING, AND MOISTURE EXISTS ACROSS
SOUTHEAST/EAST-CENTRAL MISSOURI AND SOUTHWEST ILLINOIS (COINCIDENT
WITH WHERE ANOMALOUS INTEGRATED WATER VAPOR TRANSPORT). WHILE THERE
IS A CHANCE FOR RAIN AREAWIDE SATURDAY, THE BEST CHANCES (60-80%)
EXIST IN THAT AREA, WHERE AS MUCH A 0.25 TO 0.50 INCHES IS FORECAST.
OUTSIDE OF THAT, LIGHT AND INTERMITTENT RAIN CAN BE EXPECTED. MODEL
SOUNDINGS CONTINUE TO BE LACKLUSTER IN TERMS OF THUNDERSTORM
CHANCES, LARGELY DUE TO THE LACK OF COOLING ALOFT AND SATURATED
COLUMN. WHILE AN ERRANT THUNDERSTORM OR TWO CAN'T BE RULED OUT,
THOSE WILL BE FEW AND FAR-BETWEEN.
WHILE ALL OF THIS OCCURS, YET ANOTHER SHORTWAVE EJECTS INTO THE NOW
QUASI-ZONAL FLOW ALOFT AND TAKES AIM AT THE REGION. I'M NOT
CONFIDENT THAT THERE WILL BE A CLEAN BREAK BETWEEN THE RAIN/CLOUDS
ON SATURDAY AND THIS NEXT ROUND, WHICH REPRESENTS THE GREATER
POTENTIAL FOR STRONG TO SEVERE THUNDERSTORMS ON SUNDAY. WHILE THERE
ARE STILL SOME IMPORTANT DIFFERENCES IN THE EVOLUTION OF THIS WAVE,
ONE DETAIL OF NOTE IS THAT THERE SEEMS TO BE SOME CONSENSUS THAT THE
WAVE WILL BE WEAKER AND FASTER. THIS IN NO WAY INCREASES MY
CONFIDENCE THAT THIS WILL OCCUR, BUT IF THIS NOW MORE PREVALENT
SCENARIO IN THE GUIDANCE COMES TO FRUITION, IT EITHER WON'T DEVELOP
A MATURE CYCLONE IN TIME FOR US TO BE IMPACTED OR IT WILL EJECT
NORTHEAST BEFORE INSTABILITY CAN BUILD. WHAT APPEARS LIKELY (70-80%
CHANCE) IS AT LEAST A WETTING RAIN (0.10 INCHES) WILL IMPACT MOST OF
US, WITH HIGHER TOTALS AS HIGH AS 0.50 INCHES WHERE THUNDERSTORMS
OCCUR.
IN EITHER SCENARIO (QUICK/WEAK OR SLOW/STRONG), THE NORTHWEST EXTENT
OF THE SEVERE WEATHER POTENTIAL IS IN GREATEST DOUBT. WE MAY SEE
ELEVATED CONVECTION AS EARLY AS LATE SATURDAY NIGHT INTO EARLY
SUNDAY MORNING ACROSS NORTHEAST AND CENTRAL MISSOURI AMIDST
STEEPENING MID-LEVEL LAPSE RATES AND INCREASED MUCAPE (HENCE THE SPC
DAY 3 CONVECTIVE OUTLOOK'S MARGINAL RISK, DRIVEN LARGELY BY A
CONDITIONAL HAIL THREAT). THOSE FURTHER SOUTH AND EAST HAVE A BETTER
POTENTIAL FOR STRONGER CONVECTION LATER IN THE DAY. THIS IS
SUPPORTED BY CIPS SEVERE PROBABILITY GUIDANCE FROM SAINT LOUIS
UNIVERSITY, WHICH PAINTS THE HIGHER PROBABILITIES ESSENTIALLY
ALONG/SOUTH OF THE I-44 CORRIDOR IN MISSOURI AND THE I-64 CORRIDOR
IN ILLINOIS. THAT SAID, THESE PROBABILITIES ARE LARGELY DRIVEN BY
FAVORABLE THERMODYNAMICS. THE SOUTHWEST-NORTHEASAT ORIENTATION OF
THE FORCING (A COLD FRONT), SIMILARLY-ORIENTED DEEP-LAYER SHEAR
VECTORS, AND POTENTIALLY LESS-AMPLIFIED WAVE AREN'T OVERLY
IMPRESSIVE FOR ORGANIZED SEVERE CONVECTION. HOWEVER, THERE ARE
GLIMMERS OF THE WORST-CASE SCENARIO THAT STILL SHOW UP IN SOME
GUIDANCE: THAT THE FORCING IS STRONGER AND INSTABILITY MORE
ESTABLISHED. THIS CONTINUED SIGNAL, PLUS THE FAIRLY STRONG MID-LEVEL
FLOW REGARDLESS OF THE SCENARIO, BEARS CONTINUED MONITORING,
PARTICULARLY FOR THOSE IN THE SOUTHERN AND EASTERN PARTS OF THE
FORECAST AREA WHERE THE POTENTIAL SEEMS LOCALLY-HIGHEST.
REGARDLESS OF HOW SUNDAY EVOLVES, WHAT SEEMS VERY CERTAIN (90%+
CHANCE PER THE NBM AND GLOBAL ENSEMBLES) IS THAT MARCH WILL HARDLY
"GO OUT LIKE A LAMB" AS THE EXPRESSION GOES. THE COLD FRONT THAT
PASSES THROUGH ON SUNDAY WILL USHER IN NOTICABLY-COOLER AIR TO START
THE WORK WEEK AND END THE MONTH, BY AS MUCH AS 15-20 DEGREES
COMPARED TO SUNDAY. WHILE THESE VALUES ARE NOT VERY UNCOMMON FOR THE
END OF MARCH, IT WILL FEEL LIKE A SHOCK TO THE SYSTEM AFTER DAYS OF
70S TO NEAR 80 DEGREE HIGHS. IF THE WEAKER, QUICKER SHORTWAVE
SCENARIO COMES TO PASS, THERE WOULD BE A LOWER CHANCE FOR ANY POST-
FRONTAL PRECIPITATION ON MONDAY AS THE FORCING WILL ALREADY BE EAST
OF US. OWING TO THE UNCERTAINTY IN THE TROUGH STRUCTURE DESCRIBED
ABOVE, LOW (15-20%) POPS LINGER THROUGH SUNRISE MONDAY BUT MOST OF
THE DAY APPEARS DRY. A SURFACE HIGH PROMOTING THE COOLER AIR WILL
NOT STAY FOR LONG: BY TUESDAY WE RETURN TO A SLIGHTLY-WARMER
SOUTHEAST RETURN FLOW AT THE SURFACE. TEMPERATURES WARM FURTHER INTO
MID-WEEK, THOUGH ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS LOOKS
LIKELY BY THEN.
MRB
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1036 PM CDT WED MAR 26 2025
A NORTHWEST TO SOUTHEAST ORIENTED NARROW BAND OF SHOWERS IS
EXPECTED TO DEVELOP VERY EARLY THIS MORNING, HOWEVER, ITS EXACT
PLACEMENT RELATIVE TO THE TERMINALS REMAINS UNCERTAIN. CONFIDENCE
HAS INCREASED ENOUGH THOUGH IN A SHIFT IN ITS GENERAL POSITION
THAT NOW PLACES ALL OF THE LOCAL TERMINALS IN PLAY FOR POTENTIAL
IMPACTS. THESE IMPACTS ARE EXPECTED TO BE REDUCTIONS IN
VISIBILITY DUE TO PASSING SHOWERS, WITH DRIER LOW-LEVEL AIR
KEEPING CEILINGS VFR. RAIN LOOKS TO BECOME MORE PERSISTENT LATER
IN THE MORNING BEFORE TAPERING OFF AROUND MID-DAY. GIVEN THE
NARROW NATURE OF THIS BAND OF SHOWERS, IT CAN'T BE RULED OUT THAT
SOME OF THE LOCAL TERMINALS SEE LITTLE NO RAIN THROUGH THE
MORNING. SHOWER CHANCES MAY RETURN DURING THE AFTERNOON AT ANY TO
ALL OF THE LOCAL TERMINALS, HOWEVER, CONFIDENCE IS VERY LOW ON
THE TIMING AND PLACEMENT OF THIS ACTIVITY RELATIVE TO THE LOCAL
TERMINALS. WHILE THIS POTENTIAL SECOND ROUND HAS THE GREATEST
CHANCE OF THUNDERSTORMS OCCURRING, THERE IS VERY LOW CHANCE OF
THUNDERSTORMS THIS MORNING, PARTICULARLY AT KJEF AND KCOU.
ELMORE
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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